Cutting wash apparatus and method

ABSTRACT

Cutting wash apparatus includes a wash tank ( 11 ) having side walls ( 15 ) converging to an inclined lower floor (16) and containing an air agitated wash solution including a surfactant. A cyclone separator ( 27 ) receives an oil-based mud and cutting-containing slurry through inlet ( 30 ), passing mud to an outlet ( 31 ) and a cuttings-rich component to the wash tank ( 11 ). A skimmer ( 13 ) removes wash overflow and a mud and slurry fines raft floated by the agitation, and passes this to a separator ( 18 ). Separated wash liquid is aerated and returned by pump ( 19 ) to injection points ( 28, 29 ) to recycle wash and provide the agitation. An auger ( 23 ) operates in a casing ( 21 ) opening into the tank ( 11 ) and extending upward of the wash tank and having an upper end discharge outlet ( 38 ). Additional aeration and agitation air is injected through air injection bars ( 45 ).

This invention relates to a cuttings wash apparatus and method.

This invention has particular but not exclusive application to acuttings wash apparatus and method for use on drilling rigs permittingproper disposal and/or recycling of spent drilling mud compositions, andfor illustrative purposes reference will be made to such application.However, it is to be understood that this invention could be used inother applications, such as entrained particulates washes generallygenerally.

PRIOR ART

Unless explicitly indicated to the contrary, none of the following priorart constitutes common general knowledge in the art.

The current processing systems for the capture of drill cuttingscontaminated with drilling mud are generally very large and are suitableonly for terrestrial sites. They are generally impractical to operate oneither platforms or rigs. Current practice on platforms and rigsgenerally involves the use of skips with a ship to shore operation.Alternatively bulk storage and bulk transport are employed at asignificant cost. Centrifuge/dryer processing may be followed bytransfer of clean cutting to a skip for transport. However, where lawspermit the particulate cuttings waste is dumped overboard on economicgrounds.

The main problem in the application of terrestrial apparatus and methodsto platform and rig situations is processing during drilling in realtime. Generally a rig produces around 20-24 tonnes of exhausted muds perhour at 350 feet per hour rate of penetration (ROP) of a 12¾″ drill

Several solutions are in experimentation or early adoption. Options likecuttings re-injection (CRI) are known but very expensive. Microwaveprocessing is under investigation but is scalable to about 5 tonnes perhour. The current dryers and the like work very well but the drillingprocess guarantees a huge variance in the material to be processed, thusthe units tend to struggle with screens binding up and otherthroughput-related process issues.

There is accordingly a need for a cuttings wash system suitable fordrilling platforms and rigs, which maximises the performance ofavailable equipment, minimises waste and its associated costs andoperates at real time speed relative to the drilling operation.

DESCRIPTION OF INVENTION

As used herein the word “comprising” and its parts is to be taken asnon-exclusive, unless context indicates clearly to the contrary. Thisinvention in one aspect resides broadly in cutting wash apparatusincluding:

a wash tank having side walls at least the lower portions of whichconverge to an inclined lower floor and containing an air agitated washsolution including a surfactant;

a cyclone separator adapted to receive an oil-based mud andcutting-containing slurry and passing a particulates-rich separatedcomponent of said slurry to said wash tank;

a skimmer operable to remove a raft formed at the surface of the washsolution including emulsified oil based mud and slurry fines floated bysaid agitating;

an auger casing below said inclined floor and opening into said tank ata lower portion of the floor, the auger casing extending upward of a topof the wash tank and having an discharge outlet toward its upper end;and

an auger located in the auger casing and extending from the opening intosaid inclined floor to said discharge outlet.

The wash tank may be of a hopper or hod-like configuration. For examplethe wash tank may have a generally rectangular upper portion having apair of side walls that converge downward and are closed together by theinclined floor forming both front and lower closure for the tank. Therear of the tank may have an end wall which is substantially vertical orwhich converges with the opening into the inclined floor at its lowerend to guide washed cuttings into the opening.

The wash solution will be selected according to the nature of thecontinuous phase entraining the drill cuttings. For example in the caseof oil based muds (OBM), the mud residue requires the use of a waterwash containing surfactants to clean the bulk of the mud residue fromthe cuttings. The water wash may be made up with a surfactantcomposition selected from cationic surfactants selected to wet oily clayparticles. The water wash may be selected to work in salt water. The airinjection/surfactant combination may be selected in order to promotefroth flotation of especially clay minerals cleaned from the drillcuttings.

The auger may be a shaftless auger. The auger is preferably driven fromits upper end.

The cyclone separator may be mounted directly to the wash tank or itssupporting structure in order that it may discharge separated cuttingsdirectly into the wash tank. The cyclone separator may be internallyscreened to separate residual particulates from the mud overflow. Thismud is directed directly back to mud tanks for re-blending and re use.For example, the inlet to the cyclone separator may be a tangentiallydirected inlet directing flow in the direction of rotation of thecyclone action. The tangential flow may impinge on a curved screenwhereby the entrained cuttings are screened to the cyclone underflow andthe spent mud directed to the cyclone overflow.

The cyclone separator may be in the form of a simple turret fitted tothe wash tank and screened internally with a replaceable mesh liner. Thecuttings and mud may enter tangentially and the inertia sees the mudexpelled through the mesh liner where it is collected and redirected viagravity into a mud reprocessing tank. With inertia spent, the cuttingsmay fall under their own weight into the wash tank. The screen plays aminor part during normal operation but comes to play a significant rolewhen drilling trips or a shaker screen breaks and the system has to copewith a large inflow of mud relative to the cuttings load.

The cyclone separator may be selected to match the particular chargecharacteristics of the slurry delivery system. For example, the slurrydelivery system may involve the use of a slurry pump such as thatdescribed in WO 2006/037186.

The pump may consist of a pressure vessel, an inlet nozzle, and anejector nozzle by which vacuum and pressure are applied, and an outletnozzle, in this case connected via a discharge line connected to theinlet of the cyclone separator line. The inlet and outlet nozzles areselectively closed by interconnected knife gate valves, operated intandem by a pneumatic cylinder whereby when one valve is closed, theother is open, and vice-versa. An ejector valve located in the ejectornozzle alternately creates vacuum and generate air flow through thevessel. The air from the ejector may be introduced into the dischargeline after closure of the outlet valve, if the discharge line requiresthe boost.

Drilling mud entraining cuttings may be captured by the pump via eithera gravity feed from a hopper or alternatively under vacuum.

The pump may deliver the slurry in a pump-and-fill cycle. Accordinglythe cyclone separator is preferably selected as to static capacity andthroughput to match the discharge rate of the pump. In the case of thepump described above, it is preferable that the throughput of thecyclone be in the region of 24 tonnes per hour.

Cuttings in the wash tank pass under gravity along the inclined floorand into the path of the auger through the lower opening. The cuttingsare exposed to agitation which enhances the wash effect. The airagitation may be provided by air injection a bottom portion of the washtank from a compressed air supply. Alternatively, or in addition, thewash solution may be recycled and the recycled wash solution and aircombined and injected along the inclined floor to provide the agitation.

Air bubbles from the agitation entrains emulsified oil based mud andother pollutants to form a raft at the surface of the wash solution tobe removed by a skimmer. The skimmer may comprise an overflow systemwhereby floating sludge and wash liquid is delivered to separator meanswhereby the sludge may be stripped and the polished wash liquid returnedby pump to the wash tank. For example, the overflow may pass into a tankacross a stripper belt trapping sludge on top of the belt and allowingthe polished wash liquid to pass through the belt. The belt may be aone-pass disposable web or a strippable recirculating web. The recycledwash solution may again be entrained with air and injected along theinclined floor to provide the agitation.

Drag through losses of the wash liquid to either the sludge removal orauger delivery of washed cuttings may be made up by any suitable means.For example, making up may be done in the sludge separator or the washtank

Washed cuttings may be slowly transported up the auger. This dewatersthe cuttings allowing solution to drain back into the main body of thetank.

The cuttings may be delivered from the auger outlet either directly orindirectly to a dryer assembly. The dryer may receive cuttings as auniform continuous feed at a controlled rate because the cyclone andwash actions smooth out the pulsed delivery from the preferred pump. Thedryer's operational performance band is preferably honed allowingoptimum performance to be achieved and maintained throughout the entireoperation.

Cuttings may now be discharged from the dryer and depending onenvironmental constraints can be returned to the ocean floor oralternatively transported back to shore for further processing.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that this invention may be more readily understood and put intopractical effect, reference will now be made to the accompanyingdrawings which illustrate a preferred embodiment of the invention andwherein:

FIG. 1 is a side view of apparatus in accordance with the presentinvention;

FIG. 2 is a front view of the general arrangement of a pump for use withthe apparatus of FIG. 1; and

FIG. 3 is a side view of the pump of FIG. 2.

DESCRIPTION OF THE EMBODIMENT

In the figures, there is provided a cuttings wash apparatus including asupporting, crane hoistable frame 10 supporting a wash tank 11 and auger12 assembly. The top of the tank 11 is provided with an overflow skimmerassembly 13. Remote from the supporting frame 10 there is provided apump assembly 14 as illustrated in FIGS. 3 and 4.

The wash tank 11 has a pair of opposed side walls 15 that converge tomeet an inclined floor portion 16 which forms both front and bottom wallof the tank 11. An inclined rear wall 17 closes the back of the tank.The cuttings settle passing across the inclined floor portion 16 to alower opening 20.

The lower opening 20 admits the cuttings to an auger housing 21 mountedbeneath the floor portion 16 and extending to an upper portion 22 abovethe level of the tank 11 top. The auger housing 21 contains an auger 23which is driven from its upper end by a motor and gearbox assembly 24.

The wash liquor 25 includes a cationic surfactant/flotation agent whichcauses the oil component of OBM to float as a raft 26 with othercontaminants to be skimmed off by the overflow skimmer assembly 13. Thesurfactant composition of this example is capable of use in salt waterand comprises 220 ppm Wildcat Concentrate (Wildcat Chemicals AustraliaPty Ltd) of notional composition:

Chemical Components Cationic surfactant 20-25%  d-Limonine 0-5% AceticAcid 0-2% Monobutyl Glycol Ether 0-15%  Sodium hexametaphosphate 0-2%Monoethylene Glycol 0-5% Water Balance

A wash recycle tank 18 takes wash liquid and sludge from the overflowskimmer 13 and separates the sludge to waste, entrains air and pumps thepolished wash liquid via pump 19 to the tank 11. Part of the recycledliquid is returned via upper port 28 to cuttings passing into the tankand part is directed through lower port 29 to a pair of spaced,longitudinal agitator bars 44 each having a plurality of approximately1.0 mm agitator holes. Wash liquid and entrained air projected from theagitator holes agitates the cuttings passing down the tank floor 6 toprovide agitation, wash enhancement and flotation raft formation.Further agitation and froth flotation action is provided by airinjection through port 39 to a pair of spaced, longitudinal injectionbars 45 each having a plurality of approximately 0.2 mm air injectionholes.

A cyclone separator 27 comprises a cylindrical turret having atangential slurry inlet 30 through which slurry passes from the slurrypump 14 to impinge on a curved screen, allowing cuttings to drop intothe tank 11 while the mud passes centrifugally about the turret to a mudexit 31 to reclamation and blending.

The slurry inlet 30 is connected to the outlet 32 of the pump assembly14 via a flexible hose (not shown). The pump comprises a steel vessel 34having a tapered lower body 35 to the outlet 32 which has a knifegatevalve closure 28. The vessel has an inlet 36 controlled by an inletknifegate valve 37 operated in concert with the outlet knifegate valve28 to effect cycling of the pump. An ejector assembly 40 includes acompressed air supply 41 feeding an internal venturi which isselectively valved whereby it depresses the housing via conduit 42 whenthe inlet knifegate 37 is open and the outlet knifegate valve 28 isclosed to charge the vessel 34 and pressurizes the vessel when the inletknifegate 37 is closed and the outlet knifegate valve 28 is open todischarge the vessel into the slurry inlet 30.

The pump assembly has a pallet frame assembly 43 and may be moved byforklift.

Washed cuttings are slowly transported up the auger 23 which dewatersthe cuttings allowing solution to drain back into the main body of thetank 11. The cuttings are then delivered directly into a dryer assembly(not shown) via gravity outlet 38 which now receives a uniformcontinuous feed at a controlled rate. The dryer's operationalperformance band has been honed allowing optimum performance to beachieved and maintained throughout the entire operation.

Cuttings are now discharged from the dryer assembly 13 and depending onenvironmental constraints can be returned to the ocean floor oralternatively transported back to shore for further processing.

The main objectives of this system are:

1. To reduce the amount of contaminants entering the environments wherezero discharge limits do not apply.2. To facilitate the removal of a significant amount of OBM andassociated contaminants from the drill cuttings at “real time” drillingrates (Approx 24 tonnes per hour)3. To deliver drill cuttings for further on shore processing whereby theassociated volume and costs have been significantly reduced.4. To deliver a cost effective “real time” process significantlyenhancing current global practices.

Each of the components below work at their optimum at 25 tonnes perhour, and the methodology ensures each is delivering just that.

It will of course be realised that while the above has been given by wayof illustrative example of this invention, all such and othermodifications and variations thereto as would be apparent to personsskilled in the art are deemed to fall within the broad scope and ambitof this invention as defined in the following claims.

1. Cutting wash apparatus including: a wash tank having side walls atleast the lower portions of which converge to an inclined lower floorand containing an air agitated wash solution including a surfactant; acyclone separator adapted to receive an oil-based mud andcutting-containing slurry and passing a particulates-rich separatedcomponent of said slurry to said wash tank; a skimmer operable to removea raft formed at the surface of the wash solution including emulsifiedoil based mud and slurry fines floated by said agitation; an augercasing below said inclined floor and opening into said tank at a lowerportion of the floor, the auger casing extending upward of a top of thewash tank and having an discharge outlet toward its upper end; and anauger located in the auger casing and extending from the opening intosaid inclined floor to said discharge outlet.
 2. Cutting wash apparatusaccording to claim 1, wherein the wash tank is of a hopper or hod-likeconfiguration.
 3. Cutting wash apparatus according to claim 2, whereinthe wash tank has a generally rectangular upper portion having a pair ofside walls that converge downward and are closed together by theinclined floor forming both front and lower closure for the tank. 4.Cutting wash apparatus according to claim 2, wherein the rear of thetank has an end wall selected from a substantially vertical wall and awall which converges with the opening into the inclined floor at itslower end to guide washed cuttings into the opening.
 5. Cutting washapparatus according to claim 1, wherein the slurry includes an oil basedmud and wherein the wash solution is a water wash containing cationicsurfactants.
 6. Cutting wash apparatus according to claim 1, wherein theauger is a shaftless auger.
 7. Cutting wash apparatus according to claim6, wherein the auger is driven from its upper end.
 8. Cutting washapparatus according to claim 1, wherein the cyclone separator is mounteddirectly to the wash tank.
 9. Cutting wash apparatus according to claim8, wherein the cyclone separator is internally screened to separateresidual particulates from a mud overflow.
 10. Cutting wash apparatusaccording to claim 8, wherein the inlet to the cyclone separator is atangentially directed inlet directing flow in the direction of rotationof the cyclone action.
 11. Cutting wash apparatus according to claim 10,wherein the tangential flow impinges on a curved screen whereby theentrained cuttings are screened to the cyclone underflow and the spentmud directed to the cyclone overflow.
 12. Cutting wash apparatusaccording to claim 9, wherein the cyclone separator is a turret fittedto the wash tank and with the internal screen is a replaceable meshliner, whereby the inertia of the tangential flow sees the mud expelledthrough the mesh liner where it is collected and redirected via gravityinto a mud reprocessing tank, whereupon the cuttings fall under theirown weight into the wash tank.
 13. Cutting wash apparatus according toclaim 1, wherein the cyclone separator receives slurry from pumpapparatus including: a housing having an inlet for admitting to thehousing a material to be pumped, and a delivery outlet connected to theinlet of said cyclone separator; a valve on each of said inlet and saidoutlet; control means adapted to selectively open and close respectivesaid valves; pressure reduction means under the control of said controlmeans and adapted to reduce the pressure in said housing while saidinlet valve is open to admit said material to said housing, said controlmeans being adapted to close said inlet gate means on admission of aselected charge of said material to said housing; and pressurizing meansunder the control of said control means and adapted to increase thepressure in said housing while said outlet valve is open to dischargesaid material from said housing to said cyclone separator.
 14. Cuttingwash apparatus according to claim 13, wherein the cyclone separator isselected as to static capacity and throughput to match the dischargerate of the pump.
 15. Cutting wash apparatus according to claim 1,wherein said air agitation is provided by air injection to a bottomportion of the wash tank from a compressed air supply.
 16. Cutting washapparatus according to claim 1, wherein the wash solution is recycledand wherein recycled wash solution and air are combined and injectedalong the inclined floor to provide said air agitation.
 17. Cutting washapparatus according to claim 16, wherein the skimmer comprises anoverflow system whereby floating sludge and was liquid is delivered toseparator means whereby the sludge is stripped and the polished wasliquid returned by pump to the wash tank.
 18. Cutting wash apparatusaccording to claim 17, wherein the recycled wash solution and air arecombined and injected along the inclined floor to provide saidagitation.